sensors Mode-S transponder
A1F2B1
ICAO 24-bit transponder address · allocated to United States
Currently assigned to N2243U · BOEING 777-300ER · operated by UNITED AIRLINES INC
- Hex
- A1F2B1
- Octal
- 50371261
- Decimal
- 10,613,425
- Country
- US
- Tail
- N2243U
- Type
- B77W
- Flights observed
- 116
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- 4h ago
Last known position
Country allocation
The ICAO 24-bit address A1F2B1 falls within the block assigned to United States (US) by ICAO Annex 10, Volume III. Every aircraft registered in United States receives a permanent address from this block at the time of registration; the address stays with the airframe even if the aircraft is re-registered to a different operator within the country.
Callsign history 20 distinct
| Callsign | Airline | Flights | Last seen |
|---|---|---|---|
| UAL857 | United Airlines | 10 | 2026-05-24 |
| UAL869 | United Airlines | 8 | 2026-05-14 |
| UAL189 | United Airlines | 8 | 2026-05-13 |
| UAL1844 | United Airlines | 8 | 2026-04-18 |
| UAL1149 | United Airlines | 7 | 2026-04-15 |
| UAL862 | United Airlines | 6 | 2026-05-28 |
| UAL988 | United Airlines | 5 | 2026-04-16 |
| UAL872 | United Airlines | 5 | 2026-05-22 |
| UAL190 | United Airlines | 5 | 2026-05-14 |
| UAL989 | United Airlines | 4 | 2026-04-18 |
| UAL951 | United Airlines | 4 | 2026-04-17 |
| UAL950 | United Airlines | 4 | 2026-04-17 |
| UAL878 | United Airlines | 4 | 2026-05-15 |
| UAL877 | United Airlines | 4 | 2026-05-27 |
| UAL871 | United Airlines | 4 | 2026-05-21 |
| UAL858 | United Airlines | 4 | 2026-05-25 |
| UAL43 | United Airlines | 3 | 2026-04-18 |
| UAL42 | United Airlines | 3 | 2026-04-16 |
| UAL838 | United Airlines | 2 | 2026-05-23 |
| UAL837 | United Airlines | 2 | 2026-05-22 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-05-29 | UAL79 | EWR → NRT | May 29, 20:10 UTC | May 29, 22:55 UTC | 2h 45m |
| 2026-05-29 | UAL79 | EWR → NRT | May 29, 16:10 UTC | May 29, 20:05 UTC | 3h 55m |
| 2026-05-29 | UAL2416 | LAS → SFO | May 29, 08:20 UTC | May 29, 13:00 UTC | 4h 40m |
| 2026-05-28 | UAL862 | HKG → SFO | May 28, 03:55 UTC | May 28, 16:05 UTC | 12h 10m |
| 2026-05-27 | UAL877 | SFO → HKG | May 27, 08:10 UTC | May 27, 21:35 UTC | 13h 25m |
| 2026-05-26 | UAL810 | PHL → DEN | May 26, 13:41 UTC | May 27, 01:42 UTC | 12h 1m |
| 2026-05-26 | UAL810 | PHL → DEN | May 26, 13:45 UTC | May 27, 01:49 UTC | 12h 5m |
| 2026-05-25 | UAL809 | SEA → IAD | May 25, 21:40 UTC | May 26, 10:54 UTC | 13h 15m |
| 2026-05-25 | UAL858 | ICN → SFO | May 25, 05:30 UTC | May 25, 15:10 UTC | 9h 40m |
| 2026-05-24 | UAL857 | ICN → PVG | May 24, 06:25 UTC | May 25, 06:15 UTC | 23h 50m |
| 2026-05-23 | UAL857 | ICN → PVG | May 23, 20:57 UTC | May 24, 09:09 UTC | 12h 12m |
| 2026-05-23 | UAL857 | ICN → PVG | May 23, 20:45 UTC | May 23, 21:45 UTC | 1h 0m |
| 2026-05-23 | UAL838 | NRT → SFO | May 23, 08:55 UTC | May 23, 17:40 UTC | 8h 45m |
| 2026-05-22 | UAL837 | SFO → NRT | May 22, 20:20 UTC | May 23, 06:35 UTC | 10h 14m |
| 2026-05-22 | UAL872 | TPE → SFO | May 22, 13:05 UTC | May 22, 13:40 UTC | 35m |
| 2026-05-22 | UAL872 | TPE → SFO | May 22, 02:15 UTC | May 22, 02:30 UTC | 15m |
| 2026-05-21 | UAL871 | SFO → TPE | May 21, 10:25 UTC | May 21, 10:45 UTC | 20m |
| 2026-05-20 | UAL871 | SFO → TPE | May 20, 22:00 UTC | May 20, 22:20 UTC | 20m |
| 2026-05-19 | UAL858 | ICN → SFO | May 19, 05:30 UTC | May 19, 15:00 UTC | 9h 30m |
| 2026-05-18 | UAL857 | ICN → PVG | May 18, 06:20 UTC | May 19, 06:15 UTC | 23h 54m |
| 2026-05-17 | UAL857 | ICN → PVG | May 17, 20:25 UTC | May 18, 07:20 UTC | 10h 55m |
| 2026-05-17 | UAL862 | HKG → SFO | May 17, 05:00 UTC | May 17, 16:20 UTC | 11h 20m |
| 2026-05-17 | UAL862 | HKG → SFO | May 17, 04:10 UTC | May 17, 04:25 UTC | 15m |
| 2026-05-16 | UAL877 | SFO → HKG | May 16, 07:05 UTC | May 16, 21:20 UTC | 14h 15m |
| 2026-05-15 | UAL878 | HKG → SFO | May 15, 14:45 UTC | May 16, 02:40 UTC | 11h 54m |
| 2026-05-14 | UAL869 | SFO → HKG | May 14, 20:33 UTC | May 15, 10:04 UTC | 13h 31m |
| 2026-05-14 | UAL869 | SFO → HKG | May 14, 20:50 UTC | May 15, 10:15 UTC | 13h 25m |
| 2026-05-14 | UAL190 | IAH → MIA | May 14, 00:45 UTC | May 14, 12:35 UTC | 11h 50m |
| 2026-05-13 | UAL189 | CLE → PHX | May 13, 07:45 UTC | May 13, 21:15 UTC | 13h 30m |
| 2026-05-13 | UAL189 | CLE → PHX | May 13, 07:44 UTC | May 13, 21:14 UTC | 13h 30m |
| 2026-05-12 | UAL838 | NRT → SFO | May 12, 08:20 UTC | May 12, 17:10 UTC | 8h 50m |
| 2026-05-11 | UAL837 | SFO → NRT | May 11, 19:10 UTC | May 12, 05:20 UTC | 10h 10m |
| 2026-05-11 | UAL190 | IAH → MIA | May 11, 01:01 UTC | May 11, 12:25 UTC | 11h 24m |
| 2026-05-11 | UAL190 | IAH → MIA | May 11, 00:54 UTC | May 11, 01:25 UTC | 30m |
| 2026-05-10 | UAL189 | CLE → PHX | May 10, 07:44 UTC | May 10, 21:31 UTC | 13h 47m |
| 2026-05-10 | UAL189 | CLE → PHX | May 10, 07:45 UTC | May 10, 22:15 UTC | 14h 30m |
| 2026-05-09 | UAL878 | HKG → SFO | May 9, 14:45 UTC | May 10, 02:55 UTC | 12h 10m |
| 2026-05-08 | UAL869 | SFO → HKG | May 8, 20:45 UTC | May 9, 11:15 UTC | 14h 30m |
| 2026-05-08 | UAL858 | ICN → SFO | May 8, 05:24 UTC | May 8, 14:50 UTC | 9h 25m |
| 2026-05-07 | UAL857 | ICN → PVG | May 7, 06:35 UTC | May 8, 06:14 UTC | 23h 40m |
| 2026-05-06 | UAL857 | ICN → PVG | May 6, 20:22 UTC | May 7, 09:18 UTC | 12h 56m |
| 2026-05-06 | UAL857 | ICN → PVG | May 6, 21:00 UTC | May 7, 08:10 UTC | 11h 10m |
| 2026-05-04 | UAL862 | HKG → SFO | May 4, 04:44 UTC | May 4, 16:55 UTC | 12h 10m |
| 2026-05-03 | UAL877 | SFO → HKG | May 3, 06:25 UTC | May 3, 20:45 UTC | 14h 20m |
| 2026-05-02 | UAL878 | HKG → SFO | May 2, 14:45 UTC | May 3, 03:10 UTC | 12h 25m |
| 2026-05-01 | UAL869 | SFO → HKG | May 1, 21:00 UTC | May 2, 11:35 UTC | 14h 36m |
| 2026-05-01 | UAL869 | SFO → HKG | May 1, 20:52 UTC | May 2, 11:28 UTC | 14h 36m |
| 2026-05-01 | UAL858 | ICN → SFO | May 1, 05:30 UTC | May 1, 15:10 UTC | 9h 40m |
| 2026-04-30 | UAL857 | ICN → PVG | Apr 30, 06:20 UTC | May 1, 06:15 UTC | 23h 55m |
| 2026-04-29 | UAL857 | ICN → PVG | Apr 29, 20:25 UTC | Apr 30, 07:40 UTC | 11h 14m |
About Mode-S
A Mode-S transponder code (also called an "ICAO 24-bit address" or "hex code") is a 6-character hexadecimal identifier permanently assigned to an aircraft when it's first registered. Unlike callsigns (which change with each flight) or registrations (which can change if an aircraft is sold internationally), the Mode-S address stays with the airframe for the life of the aircraft in that country.
Every ADS-B transmission from an aircraft includes its Mode-S address, making it the most reliable way to identify a specific airframe. Flight-tracking services like Apparatus use the Mode-S address as the primary key for tying position broadcasts, callsigns, and ownership records together.
Prefer a tail-number view? See the N2243U page for operator, model, and routing details .